A method for preparing high-purity brominated polystyrene via a full bromination process

Abstract

This invention discloses a method for preparing high-purity brominated polystyrene by a full bromine method, which relates to the field of polymer chemistry. By introducing a p-tert-butylcalix[4] aromatic derivative as a regioselective directing agent in the compounding process of the catalytic directing system, its bowl-shaped hydrophobic cavity structure forms a non-covalent complex with the side benzene ring of polystyrene through π-π stacking interaction, achieving precise anchoring of para sites and physical shielding of adjacent sites. Combined with the stabilizing effect of the spatial confinement effect on the bromium ion intermediate, the molar ratio of para-bromine is greatly increased. Moreover, the amount of directing agent added is only 0.05%-0.2% of the mass of polystyrene. Based on the non-covalent effect, it can be completely removed by precipitation and rinsing steps without introducing residual impurities. The bromine content of the product is stable at more than 66%.

Description

Technical Field

[0001] This invention relates to the field of polymer chemistry, specifically to a method for preparing high-purity brominated polystyrene via a full bromine process. Background Technology

[0002] The perbromination process is currently the mainstream industrial process for producing brominated polystyrene. It uses polystyrene as raw material and elemental bromine as the brominating agent. Under Lewis acid catalysis, an electrophilic substitution reaction of the benzene ring occurs. This process has a short route, high bromine utilization rate, and the bromine content of the product can reach more than 66%, which meets the performance requirements of high-end flame retardant applications. In order to suppress the bromination side reaction of the tertiary carbon sites of the main chain and the degradation of the molecular chain, existing processes generally combine main chain inhibitors, which can effectively improve the mechanical retention and thermal stability of the product.

[0003] However, in existing technologies, conventional Lewis acids can only enhance the reactivity of bromination reactions and cannot precisely control the substitution region of bromine atoms on the benzene ring. The molar ratio of para-bromination to ortho-bromination in the product is usually stable at around 55:45, with a low para-substitution ratio. The ortho-bromine atom is affected by the steric hindrance and electronic effects of the methylene side chain, resulting in a lower C-Br bond energy than the para structure. During high-temperature processing, it is prone to debromination and decomposition, which not only leads to a decrease in the long-term thermal stability of the product but also corrodes the screw and die of the processing equipment. At the same time, the ortho structure will disrupt the regularity of the molecular chain, reduce the melting point and crystallinity of the product, and limit its application in high-temperature processed engineering plastics.

[0004] Currently, there are very limited optimization methods for the regioselectivity of bromination. Adjusting the type of catalyst, reaction temperature, or solvent polarity can only cause the para-position ratio to fluctuate by 3%-5%, which cannot achieve a significant increase. Furthermore, using modified raw materials with substituent positioning will greatly increase costs and damage the polystyrene backbone structure. Summary of the Invention

[0005] The purpose of this invention is to make up for the shortcomings of the prior art and provide a method for preparing high-purity brominated polystyrene by the all-bromine method. By introducing p-tert-butylcalix[4] aromatic derivative as a regioselective directing agent in the compounding process of the catalytic directing system, the bowl-shaped hydrophobic cavity structure is used to form a non-covalent complex with the side benzene ring of polystyrene through π-π stacking interaction, so as to achieve precise anchoring of para site and physical shielding of adjacent site. Combined with the stabilizing effect of spatial confinement on the bromium ion intermediate, the molar ratio of para-bromine is greatly increased.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing high-purity brominated polystyrene by a full bromination method, the method comprising the following specific steps: S1: Dissolve the polystyrene raw material in a halogenated hydrocarbon solvent to prepare a polystyrene solution with a mass concentration of 5%-15%; S2: Add Lewis acid catalyst, main chain inhibitor and regioselective directing agent to polystyrene solution and stir until homogeneous; the regioselective directing agent is a p-tert-butylcalix[4] aromatic derivative, and the amount added is 0.05%-0.2% of the mass of polystyrene; S3: Under light-protected conditions and at 0-25℃, bromine is added dropwise to the reaction system to induce the bromination of the benzene ring. After the addition is complete, the reaction is kept at the temperature for 2-6 hours. S4: After the reaction is complete, the product is quenched, washed with water, separated, precipitated, and dried to obtain a high-purity brominated polystyrene product.

[0007] Further, in step S1, polystyrene raw material is added to a reaction vessel equipped with a mechanical stirrer, a halogenated hydrocarbon solvent is added, the system temperature is controlled at 20-30℃, the stirring speed is set to 200-300 rpm, and stirring is carried out for 30-60 minutes until the solid is completely dissolved, resulting in a clear and transparent polystyrene solution. The solution mass concentration is controlled at 5%-15%, and the polystyrene used is general-purpose grade polystyrene with a weight-average molecular weight of 8×10⁻⁶. 4 -2×10 5 Concentrations below 5% will reduce production efficiency, while concentrations above 15% will lead to excessively high system viscosity, uneven dispersion of additives, and hindered mass transfer in the bromination reaction. The halogenated hydrocarbon solvent is selected from at least one of dichloromethane, 1,2-dichloroethane, chloroform, carbon tetrachloride, and chlorobenzene; Dissolving polystyrene fully in a halogenated hydrocarbon solvent creates a homogeneous reaction system, ensuring that subsequent catalysts, inhibitors, and directing agents can fully contact the benzene rings on the side of the polystyrene. This avoids reaction inhomogeneity and selectivity fluctuations caused by solid-liquid heterogeneity. Halogenated hydrocarbons are chosen as solvents because they have excellent solubility for polystyrene, achieving high substrate concentrations at low viscosity. Furthermore, halogenated hydrocarbons are chemically stable under bromination reaction conditions and do not react with bromine or Lewis acids. Their moderate polarity can also moderately stabilize the bromium ion reaction intermediate, ensuring the smooth progress of the electrophilic substitution reaction.

[0008] Furthermore, in step S2, a main chain inhibitor is added to the polystyrene solution and stirred at 200-250 rpm for 5-10 minutes until uniformly dispersed; the main chain inhibitor is selected from at least one of phosphorous acid, hypophosphite, tri-n-butylphosphine, and dimethyl sulfoxide, and the amount added is 0.5%-2% of the mass of polystyrene; After the main chain inhibitor is evenly dispersed, add the Lewis acid catalyst and continue stirring for 10-15 minutes until the catalyst is completely dispersed and dissolved. The Lewis acid catalyst is selected from at least one of aluminum trichloride, aluminum tribromide, ferric chloride, ferric tribromide, and tin tetrachloride, and the amount added is 1%-5% of the mass of polystyrene. After the Lewis acid catalyst is completely dissolved, add the regioselective directing agent and stir continuously for 15-20 minutes. The regioselective directing agent is a p-tert-butylcalix[4] aromatic derivative, and the amount added is 0.05%-0.2% of the mass of polystyrene.

[0009] Furthermore, the p-tert-butylcalix[4] aromatic derivative is selected from at least one of p-tert-butylcalix[4] aromatics, p-tert-butylcalix[4] aromatics-25,27-dimethyl ether, and p-tert-butylcalix[4] aromatics tetraethyl ethyl acetate.

[0010] Furthermore, main chain inhibitors can quench trace amounts of free radical active species in the reaction system through reduction or coordination, while weakening the activation ability of Lewis acids on the tertiary carbon sites of the main chain. This effectively inhibits bromination side reactions and molecular chain breakage degradation on the main chain, ensuring the stability of the product's molecular weight and mechanical properties.

[0011] Lewis acids can coordinate with bromine, polarize bromine molecules and generate highly reactive bromium ion intermediates, thus promoting efficient bromination reactions. Due to the combined effects of the electronic and steric effects of the benzene ring itself, bromine atoms naturally tend to undergo mixed substitution at the ortho and para positions without directional regulation, with a ratio close to 45:55.

[0012] The tert-butylcalix[4] aromatic derivative has a bowl-shaped hydrophobic cavity structure. Its molecular skeleton is rich in benzene ring units. The aromatic ring structure at its upper edge can form a stable non-covalent complex with the benzene ring side group on the polystyrene side chain through π-π stacking interaction, so that the calix aromatic cavity is precisely anchored in the outer space of the benzene ring. The cup-shaped cavity has a clear spatial size and fixed orientation. Its opening direction is directly opposite the para reaction site of the benzene ring. At the same time, it physically shields the adjacent reaction site through the steric hindrance effect of its own molecular skeleton. The electron-rich environment inside the cavity can also stabilize the bromium ion intermediate entering the cavity, reduce the reaction activation energy of bromium ion attacking the para site, and make the bromination reaction preferentially generate the para-substituted product.

[0013] Furthermore, when the amount of directing agent is less than 0.05% of the mass of polystyrene, the calixarene molecules are isolated and dispersed on the polystyrene molecular chain, and the π-π stacking effect is insufficient to form an effective shielding network for adjacent sites, so the increase in para site ratio is limited. When the amount reaches 0.05%, the directing agent molecules gradually form a continuous supramolecular covering layer on the side group surface of the benzene ring, producing a synergistic shielding effect, and the para site ratio jumps. When the amount exceeds 0.2%, multilayer physical adsorption leads to an increase in reaction mass transfer resistance and a slight decrease in yield. Therefore, the amount of directing agent is strictly limited to 0.05%-0.2%.

[0014] Furthermore, in step S3, the outer wall of the reaction vessel is wrapped with a light-shielding material to prevent bromine from decomposing into free radicals and triggering side reactions upon exposure to light; a low-temperature ice-water bath system is connected to lower the system temperature to 0-25℃ and stabilize it; bromine is added dropwise at a constant pressure dropping funnel at a uniform rate for 1-3 hours, and the system temperature fluctuation is controlled within ±1℃ by adjusting the ice-water bath flow rate during the addition process to prevent local overheating from exacerbating ortho-substitution and main chain side reactions; after the addition is completed, the set temperature is maintained for another 2-6 hours to ensure that the benzene ring bromination reaction proceeds fully.

[0015] The molar amount of bromine added should be 3.0-3.5 times the molar amount of benzene ring in polystyrene to ensure that the benzene ring reaches a high degree of bromination, mainly tribromo. If the reaction temperature is too high, it will intensify the ortho-substitution and main chain side reactions; if the temperature is too low, the reaction rate will be too slow and the production efficiency will decrease. After bromine is added to the system, it continuously generates bromium ion active intermediates under the activation of Lewis acids. These intermediates attack electron-rich sites on the benzene ring to complete electrophilic substitution reactions, gradually introducing multiple bromine atoms onto the benzene ring. The reaction rate is controlled by low temperature and uniform dropwise addition to avoid excessively high local bromine concentrations and concentrated exothermic reactions that could lead to a sudden rise in system temperature. This reduces ortho-selectivity shift and main-chain bromination side reactions caused by high temperature. Light-shielding treatment can inhibit the photolysis of bromine to generate bromine free radicals, avoiding non-selective bromination and polystyrene molecular chain breakage caused by free radical pathways, thus ensuring the stability of the product's molecular weight and regioselectivity.

[0016] Furthermore, the specific steps of S4 are as follows: While maintaining stirring, slowly add a 10% sodium sulfite aqueous solution to the reaction system. The unreacted free bromine is removed by the reducing effect of sodium sulfite. The endpoint is reached when the reddish-brown color of the organic phase completely disappears. At the same time, the Lewis acid catalyst is deactivated, thus terminating the bromination reaction. Transfer the quenched mixture to a separatory funnel and let it stand for 10-15 minutes to separate the layers. Dispose of the lower organic phase. Wash the organic phase 3-5 times with deionized water at 20-30℃, using 1 / 2-2 / 3 of the organic phase volume each time. Shake and let stand to separate the layers until the pH of the aqueous phase is 6.5-7.5 to remove catalyst residues, bromides and water-soluble additives from the system. The washed organic phase is slowly injected into 3-5 times its volume of precipitant, and the stirring speed is maintained at 300-400 rpm to allow the brominated polystyrene to be fully precipitated in solid form. The solid product is collected by vacuum filtration, and the filter cake is washed 2-3 times with precipitant, with the amount of precipitant used in each wash being 2-3 times the mass of the filter cake, in order to remove the adsorbed trace amounts of directing agent and solvent residue. The filter cake is transferred to a vacuum drying device, and the temperature is controlled at 70-90℃ and the vacuum degree is -0.08 to -0.1MPa. It is dried for 10-15 hours to completely remove residual solvent and finally obtain high-purity brominated polystyrene product.

[0017] Furthermore, the p-tert-butylcalix[4] aromatic derivative is preferably one of p-tert-butylcalix[4] aromatic, p-tert-butylcalix[4] aromatic-25,27-dimethyl ether, and p-tert-butylcalix[4] aromatic tetraethyl ethyl acetate; the Lewis acid catalyst is preferably one of ferric tribromide and aluminum trichloride; the main chain inhibitor is preferably one of phosphorous acid and hypophosphorous acid; the halocarbon solvent is preferably 1,2-dichloroethane; and the precipitant is preferably anhydrous ethanol.

[0018] Compared with existing technologies, this method for preparing high-purity brominated polystyrene via a full bromination process has the following advantages: This invention significantly increases the molar ratio of para-bromine on the benzene ring from about 55% in the traditional process to over 75% by guiding the supramolecular action of the tert-butylcalix[4] aromatic derivative. Correspondingly, the ortho-structure with poor thermal stability is greatly reduced. The temperature corresponding to a 5% thermal weight loss of the product under nitrogen atmosphere is increased from about 300℃ to over 320℃, and the high-temperature processing stability and weather resistance are substantially improved. At the same time, the amount of the guiding agent is only 0.05%-0.2% of the mass of polystyrene, and it can be completely removed in the subsequent precipitation and rinsing process. It will not form harmful residues in the product. The bromine content of the final product is stably maintained at over 66%, and the purity and thermal properties meet the requirements of high-end flame retardant applications.

[0019] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0021] Figure 1 A flowchart of a method for preparing high-purity brominated polystyrene using the all-bromine method; Figure 2 This is a flowchart of step S3 in a method for preparing high-purity brominated polystyrene using the all-bromine method. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below. Example 1

[0023] For example Figure 1 As shown, weigh 10.0g of general-purpose polystyrene (weight average molecular weight 1.0×10⁻⁶). 5 The solid (with a molecular weight distribution index of 1.8) was added to a 250 mL three-necked flask equipped with a mechanical stirrer, a constant pressure dropping funnel, and a precision thermometer. 150 mL of 1,2-dichloroethane (analytical grade, water content ≤0.05%) was added to the flask. The constant temperature water bath was turned on, the system temperature was controlled at 25 °C, and the stirring speed was set to 250 rpm. After stirring for 40 min, the solid was completely dissolved, and a colorless, clear, and transparent polystyrene solution with a mass concentration of approximately 6.25% was obtained.

[0024] Keep stirring at 250 rpm, first add 0.10 g of phosphorous acid (analytical grade, mass fraction 99%) to the solution, stir for 5 min to make it uniformly dispersed in the system; then add 0.30 g of anhydrous ferric tribromide (analytical grade), continue stirring for 10 min, the system is light brownish-yellow and there are no solid particles left; finally add 0.005 g of p-tert-butylcalix[4] aromatic hydrocarbon (purity ≥98%), continue stirring for 15 min to form a uniform and stable reaction solution.

[0025] like Figure 2 As shown, the three-necked flask was completely wrapped with aluminum foil to ensure complete light protection. The low-temperature ice-water bath device was replaced, and the system temperature was lowered to 10℃ and kept stable for 30 minutes. 49.0g of purified bromine (purity ≥99.5%, corresponding to 3.2 times the molar amount of benzene ring) was added to the constant-pressure dropping funnel, and the upper opening of the funnel was connected to the hydrogen bromide tail gas absorption device. The dropping valve was opened, and the dropping rate of bromine was controlled at about 0.41g / min. The total dropping time was 2 hours. During the dropping process, the system temperature was maintained in the range of 9-11℃ by adjusting the circulation flow rate of the ice-water bath. After the dropping was completed, the reaction was continued at 10℃ for 4 hours. In the later stage of the reaction, the system turned a uniform dark reddish-brown color.

[0026] After the reaction was complete, the stirring speed was reduced to 200 rpm. A 10% sodium sulfite aqueous solution was slowly added dropwise to the system at a rate of 5 mL / min, observing the color of the system as it was added. The addition was stopped when the reddish-brown color of the organic phase completely disappeared and the system became a pale yellow turbid liquid. The mixture was then transferred to a 500 mL separatory funnel and allowed to stand for 15 minutes to separate the layers, clearly separating the lower organic phase. 75 mL of 25°C deionized water was added to the organic phase, gently shaken, and allowed to stand for 10 minutes before separation. This washing process was repeated four times. The final pH of the aqueous phase was measured to be 7.0. The washed organic phase was then... The solution was slowly injected into a 1000 mL beaker containing 500 mL of anhydrous ethanol at a flow rate of approximately 10 mL / min, while continuously stirred at a rate of 350 rpm. After the addition was complete, stirring was continued for 30 min to allow the brominated polystyrene to precipitate completely. The product was collected by vacuum filtration using a Buchner funnel. The filter cake was washed twice with anhydrous ethanol, 50 mL each time. After drying, the filter cake was transferred to a clean petri dish and placed in a vacuum drying oven at 80 °C and a vacuum of -0.09 MPa for 12 h. After drying, the product was removed, cooled to room temperature in a desiccator, and weighed to obtain a white powder product. Example 2

[0027] In this embodiment, the amount of the directing agent was adjusted to 0.01g (0.1% of the mass of polystyrene). The specifications, amounts, operating steps and process parameters of the other raw materials were completely consistent with those in Example 1, and a white powder product was finally obtained. Example 3

[0028] In this embodiment, the amount of the directing agent was adjusted to 0.02g (0.2% of the mass of polystyrene). The specifications, amounts, operating steps and process parameters of the other raw materials were completely consistent with those in Example 1, and a white powder product was finally obtained. Example 4

[0029] Weigh 10.0g of general-purpose polystyrene (weight average molecular weight 1.0×10⁻⁶). 5 The solid (with a molecular weight distribution index of 1.8) was added to a 250 mL three-necked flask equipped with a mechanical stirrer, a constant pressure dropping funnel, and a precision thermometer. 150 mL of chloroform (analytical grade, water content ≤0.05%) was added to the flask. The constant temperature water bath was turned on, the system temperature was controlled at 25 °C, the stirring speed was set to 250 rpm, and the solid was stirred for 45 min until it was completely dissolved, resulting in a colorless, clear, and transparent polystyrene solution.

[0030] Keep stirring at 250 rpm, first add 0.15 g hypophosphite (analytical grade, 50% aqueous solution) to the solution, stir for 5 min to make it evenly dispersed; then add 0.20 g anhydrous aluminum trichloride (analytical grade), continue stirring for 12 min, the system is light yellow-brown; finally add 0.015 g p-tert-butylcalix[4]arene-25,27-dimethyl ether (purity ≥98%), continue stirring for 18 min to form a homogeneous reaction solution.

[0031] Wrap the flask with aluminum foil to protect it from light. Replace the ice-water bath to lower the system temperature to 5℃ and stabilize it for 30 minutes. Add 60.0g of purified bromine (corresponding to 3.3 times the molar amount of benzene ring) to the constant pressure dropping funnel, control the dropping rate to about 0.40g / min, and the total dropping time is 2.5h. During the dropping process, the temperature is maintained at 4-6℃. After the dropping is completed, keep the reaction at 5℃ for 5h.

[0032] Quenching and purification post-treatment: After the reaction was completed, 10% sodium sulfite aqueous solution was slowly added dropwise to quench the organic phase until it decolorized; the organic phase was transferred to a separatory funnel and allowed to stand for separation. The organic phase was separated and washed three times with 75 mL of deionized water at 25 °C each time. The final aqueous phase pH was 6.8. The organic phase was injected into 600 mL of anhydrous methanol at a flow rate of about 8 mL / min and stirred at 350 rpm to precipitate a solid. After the addition was completed, stirring was continued for 30 min; after filtration, the filter cake was washed twice with 60 mL of anhydrous methanol each time; the filter cake was placed in a vacuum drying oven and dried at 75 °C and -0.09 MPa for 14 h. After cooling, a white powder product was obtained. Example 5

[0033] Weigh 10.0g of general-purpose polystyrene (GPPS, grade PG-33, weight average molecular weight 1.0×10⁻⁶). 5 1,2-dichloroethane (with a molecular weight distribution index of 1.8) was added to a 250 mL three-necked flask equipped with a mechanical stirrer, a constant pressure dropping funnel, and a precision thermometer. 150 mL of 1,2-dichloroethane was added to the flask. The mixture was stirred at 25 °C and 250 rpm for 35 min until completely dissolved, resulting in a clear solution.

[0034] Keep stirring, first add 0.08g of tri-n-butylphosphine (analytical grade), stir for 8 min; then add 0.40g of anhydrous ferric chloride (analytical grade), stir for 15 min until completely dispersed; finally add 0.01g of p-tert-butylcalix[4] ethyl acetate (purity ≥98%), and continue stirring for 20 min.

[0035] The system temperature was lowered to 15℃ and stabilized under light-protected conditions; 56.0 g of purified bromine (corresponding to 3.1 times the molar amount of benzene ring) was added to a constant-pressure dropping funnel, and the dropping rate was controlled at about 0.62 g / min, with a total dropping time of 1.5 h. The temperature was maintained at 14-16℃ during the dropping process; after the dropping was completed, the reaction was kept at 15℃ for 3 h.

[0036] After quenching with sodium sulfite aqueous solution, the organic phase was washed 5 times with 75 mL of deionized water at 25 °C until the pH of the aqueous phase was 7.2. The organic phase was then injected into 450 mL of anhydrous ethanol for precipitation, and stirred at 350 rpm. After filtration, the organic phase was washed twice with 50 mL of anhydrous ethanol each time. The product was then dried under vacuum at 85 °C and -0.09 MPa for 10 h, and after cooling, a white powder product was obtained. Comparative Example 1

[0037] This comparative example is parallel to Example 2, without the addition of p-tert-butylcalix[4] aromatic regioselective directing agent. The specifications, dosages, operating steps and process parameters of the other raw materials are completely consistent with those of Example 2. The specific steps are as follows: Weigh 10.0g of general-purpose polystyrene (weight average molecular weight 1.0×10⁻⁶). 5 The solid (with a molecular weight distribution index of 1.8) was added to a 250 mL three-necked flask equipped with a mechanical stirrer, a constant pressure dropping funnel, and a precision thermometer. 150 mL of 1,2-dichloroethane (analytical grade, water content ≤0.05%) was added to the flask. The constant temperature water bath was turned on, the system temperature was controlled at 25 °C, the stirring speed was set to 250 rpm, and the solid was completely dissolved after stirring for 40 min, resulting in a colorless, clear, and transparent polystyrene solution.

[0038] While maintaining a stirring speed of 250 rpm, first add 0.10 g of phosphorous acid (analytical grade, 99% by mass) to the solution and stir for 5 min to disperse it evenly; then add 0.30 g of anhydrous ferric tribromide (analytical grade) and continue stirring for 10 min. The system is light brownish-yellow and there are no solid particles remaining, forming a homogeneous reaction solution.

[0039] Completely wrap the outer wall and neck of the three-necked flask with aluminum foil to protect it from light. Replace the low-temperature ice-water bath device and lower the system temperature to 10℃ and maintain it at a constant temperature for 30 minutes. Add 58.0g of purified bromine (purity ≥99.5%, corresponding to 3.2 times the molar amount of benzene ring) to the constant-pressure dropping funnel. Connect the upper opening of the funnel to the hydrogen bromide tail gas absorption device. Open the dropping valve and control the bromine dropping rate to about 0.48g / min. The total dropping time is 2 hours. During the dropping process, maintain the system temperature in the range of 9-11℃. After the dropping is completed, keep the temperature at 10℃ and continue the reaction for 4 hours.

[0040] After the reaction was complete, the stirring speed was reduced to 200 rpm, and a 10% sodium sulfite aqueous solution was slowly added dropwise to the system at a rate of 5 mL / min until the reddish-brown color of the organic phase completely disappeared. The mixture was transferred to a 500 mL separatory funnel and allowed to stand for 15 min to separate the layers, separating the lower organic phase. 75 mL of 25 °C deionized water was added for washing, followed by shaking and separation. The water washing operation was repeated 4 times until the final pH of the aqueous phase was 7.0. The washed organic phase was slowly injected into a 1000 mL beaker containing 500 mL of anhydrous ethanol at a flow rate of approximately 10 mL / min. A solid precipitated under stirring at 350 rpm. After the addition was complete, stirring was continued for 30 min. The mixture was filtered through a Buchner funnel, and the filter cake was washed twice with 50 mL of anhydrous ethanol each time. The filter cake was placed in a vacuum drying oven and dried at 80 °C and -0.09 MPa for 12 h. After cooling, a white powder product was obtained. Comparative Example 2

[0041] The dosage of the directing agent in this comparative example is 0.002g (0.02% of the mass of polystyrene), which is lower than the limit of this invention. The specifications, dosages, operating steps and process parameters of the other raw materials are completely consistent with those in Example 2, and a white powder product is finally obtained. Comparative Example 3

[0042] The dosage of the directing agent in this comparative example is 0.03g (0.3% of the mass of polystyrene), which is higher than the limit of this invention. The specifications, dosages, operating steps and process parameters of the other raw materials are completely consistent with those in Example 2, and a white powder product is finally obtained.

[0043] The prepared high-purity brominated polystyrene was tested: Bromine content determination: The oxygen flask combustion-mercuric nitrate potentiometric titration method was adopted. Approximately 0.02 g of dry sample was weighed and placed in a combustion flask filled with oxygen. The sample was completely combusted to decompose the sample, and all bromine was converted into bromide ions. The decomposition products were absorbed with dilute sodium hydroxide solution. After the absorbent was diluted to volume, potentiometric titration was performed with mercuric nitrate standard solution. The mass fraction of bromine in the sample was calculated based on the volume of standard solution consumed at the titration endpoint.

[0044] Determination of the ratio of ortho- and para-bromine: The 1H NMR method was used. A sample solution with a concentration of approximately 10 mg / mL was prepared using deuterated chloroform as a solvent. The 1H NMR spectrum was acquired at room temperature using a 400 MHz NMR spectrometer. The molar ratio of para-bromine structure to ortho-bromine structure was calculated by integrating the characteristic proton peaks at different chemical shifts in the benzene ring region.

[0045] Thermal stability determination: Thermogravimetric analysis was used. Approximately 5 mg of sample was placed in an alumina crucible and heated from room temperature to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere (air flow rate of 50 mL / min). The temperature at which the sample's thermal weight loss rate reached 5% was recorded to characterize the product's thermal stability.

[0046] Product yield calculation: The formula for calculating product yield is: Product yield = (actual mass of dried product / theoretical mass of brominated product) × 100%, where the theoretical mass of brominated product is calculated based on the degree of substitution of polystyrene benzene ring with complete tribromo substitution.

[0047] The core performance test results of each embodiment and comparative example are shown in the table below: In summary, this invention introduces a trace amount of p-tert-butylcalix[4] aromatic derivative as a regioselective directing agent into the traditional all-bromine reaction system. Through supramolecular host-guest recognition and spatial confinement effect, the directional regulation of bromination sites can be achieved. Under the premise of ensuring high bromine content and high yield of the product, the para-bromination ratio of benzene ring can be increased from about 55% in the conventional process to more than 75%. The product thermal weight loss of 5% corresponds to a temperature increase of more than 20℃, and the thermal stability is significantly improved. When the amount of directing agent is controlled within the range of 0.05%-0.2% of the mass of polystyrene, it can achieve excellent regioselectivity regulation effect without introducing residual impurities that affect the purity of the product. The increase in auxiliary cost is limited, and the process is fully compatible with existing industrial production lines. It has outstanding technical advantages and good prospects for industrial application.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing high-purity brominated polystyrene via a full-bromine process, characterized in that, The method includes the following specific steps: S1: Dissolve the polystyrene raw material in a halogenated hydrocarbon solvent to prepare a polystyrene solution with a mass concentration of 5%-15%; S2: Add Lewis acid catalyst, main chain inhibitor and regioselective directing agent to polystyrene solution and stir until homogeneous; S3: Under light-protected conditions and at 0-25℃, bromine is added dropwise to the reaction system to induce the bromination of the benzene ring. After the addition is complete, the reaction is kept at the temperature for 2-6 hours. S4: After the reaction is complete, the product is quenched, washed with water, separated, precipitated, and dried to obtain a high-purity brominated polystyrene product.

2. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 1, characterized in that, In step S1, polystyrene raw material is added to a halogenated hydrocarbon solvent and stirred at 20-30°C and 200-300 rpm for 30-60 minutes until the polystyrene is completely dissolved, thus preparing a polystyrene solution with a mass concentration of 5%-15%; the halogenated hydrocarbon solvent is selected from at least one of dichloromethane, 1,2-dichloroethane, chloroform, carbon tetrachloride, and chlorobenzene.

3. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 1, characterized in that, In step S2, a main chain inhibitor is added to the polystyrene solution and stirred at 200-250 rpm for 5-10 minutes until it is evenly dispersed; the main chain inhibitor is selected from at least one of phosphorous acid, hypophosphite, tri-n-butylphosphine, and dimethyl sulfoxide, and the amount added is 0.5%-2% of the mass of polystyrene.

4. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 1, characterized in that, In step S2, after the main chain inhibitor is evenly dispersed, the Lewis acid catalyst is added and stirring is continued for 10-15 minutes until the catalyst is completely dispersed and dissolved. The Lewis acid catalyst is selected from at least one of aluminum trichloride, aluminum tribromide, ferric chloride, ferric tribromide, and tin tetrachloride, and the amount added is 1%-5% of the mass of polystyrene.

5. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 1, characterized in that, In S2, after the Lewis acid catalyst is completely dissolved, a regioselective directing agent is added and the mixture is stirred for 15-20 minutes. The regioselective directing agent is a p-tert-butylcalix[4] aromatic derivative, and the amount added is 0.05%-0.2% of the mass of polystyrene.

6. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 5, characterized in that, The p-tert-butylcalix[4] aromatic derivative is selected from at least one of p-tert-butylcalix[4] aromatics, p-tert-butylcalix[4] aromatics-25,27-dimethyl ether, and p-tert-butylcalix[4] aromatics tetraethyl ethyl acetate.

7. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 1, characterized in that, In S3, the molar amount of bromine is 3.0-3.5 times the molar amount of benzene ring structural units in polystyrene.

8. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 1, characterized in that, In S3, the reaction system temperature is controlled at 5-15℃, the bromine addition time is 1.5-2.5h, and the heat preservation reaction time is 3-5h.

9. The method for preparing high-purity brominated polystyrene by the all-bromine method according to claim 1, characterized in that, In step S4, a 10% (w / w) sodium sulfite aqueous solution is slowly added dropwise to the reaction system for quenching, until the reddish-brown color of the organic phase completely disappears. After standing and separating the layers, the organic phase is separated and washed 3-5 times with deionized water at a temperature of 20-30°C. The amount of water used for each wash is 1 / 2-2 / 3 of the volume of the organic phase, and the washing continues until the pH of the aqueous phase is neutral. The washed organic phase is then injected into 3-5 times its volume of precipitant, and a solid product is precipitated under stirring at 300-400 rpm. After filtration, the filter cake is washed 2-3 times with the precipitant. The filter cake is then placed in a vacuum drying oven at 70-90°C and a vacuum degree of -0.08 to -0.1 MPa and dried for 10-15 hours to obtain high-purity brominated polystyrene.

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